Chronic warming, not heatwaves, predicts tropical fish colonization in the Mediterranean

The opening of the Suez Canal created a new connection between the Red Sea and the Mediterranean Sea, breaking down a natural barrier that had kept the two bodies of water separated for millions of years. Researchers sought to understand whether tropical fish were arriving in the Mediterranean due to sudden increases in temperature (marine heatwaves) or because of a longer-term rise in temperatures.

After examining data on the arrival of 75 non-native fish species in the Mediterranean, the scientists found that the spread of these species was largely driven by a gradual increase in background warming. Marine heatwaves did not play a significant role in determining which species arrived or how quickly they established themselves.

Instead, the chronic warming of the Mediterranean climate acted as a continuous facilitator for the colonization of warmer-adapted fish, accelerating their expansion after they had already established themselves in the region. The Suez Canal acted as a catalyst for this significant shift in the Mediterranean's biogeography.